why is my skoda octavia vrs, not turbo-ing?

i have just acquired a 2001 y reg skoda octavia vrs. 1.8t ... but the turbo is not boosting well not working, at all. is there something simple that is a common problem. ? thanks, other than that a beautiful car.
it has been on a diagnostic machine/
and codes are 17704.and poss 17964.